Particle-fibre-agglomerates

ABSTRACT

Particle fiber agglomerates comprise fibers having the structure of individual fibers, fiber bundles, fiber tufts or mixtures thereof with firmly adhering particles.

DESCRIPTION

[0001] The present invention relates to particle-fiber agglomerates (PFAs) comprising fibers having the structure of individual fibers, fiber bundles, fiber tufts or mixtures thereof with firmly adhering particles.

[0002] There are a multiplicity of processes in which liquids or gases flow through beds of solid particles. Examples are gas drying and gas cleaning or purifying processes using fixed beds containing adsorbents or molecular sieves, water treatment in ion exchangers and especially heterogeneously catalyzed processes in which the fixed beds contain catalytically active solid particles.

[0003] In other, especially heterogeneously catalyzed processes, such as suspension catalysis, moving bed or fluidized bed processes, small catalytically active solid particles are finely dispersed in liquids or gases and removed again from the product stream.

[0004] The problem with the first processes mentioned is the use of very small solid particles to counteract diffusion barriers in the solid particles while still ensuring sufficient perviousness to liquids or gases.

[0005] With regard to the second kind of processes, where small solid particles are used to minimize diffusion barriers, the problem is to remove these small solid particles from the product stream as completely as possible.

[0006] WO-A-99/15292 discloses a method drawn to solving these problems. A three-dimensional network of metal fibers is fabricated and has applied to it very small solid particles no greater than 300 microns.

[0007] However, this method has appreciable disadvantages.

[0008] The particle size is limited to very small particles.

[0009] The fibrous network can be packed with solid particles only to a small fraction in order to leave sufficient perviousness to liquids or gases.

[0010] Thirdly, the three-dimensional fibrous networks have to be formed into shapes which have to be adapted to the particular application.

[0011] It is an object of the present invention to remedy the aforementioned disadvantages.

[0012] We have found that this object is achieved by novel particle-fiber agglomerates consisting of or comprising fibers having the structure of individual fibers, fiber bundles, fiber tufts or mixtures thereof with firmly adhering particles.

[0013] Fixed beds formed therefrom have elastic properties.

[0014] The particle-fiber agglomerates according to the invention can be prepared as follows.

[0015] Preparation Process A

[0016] Fixation of Particles with Fibers using Binders

[0017] The fibers can be dispersed in a moist mass consisting of or comprising a binder with or without a swellant. The mass obtained can be applied to the particles by stirring or kneading with the particles for example.

[0018] The drying of the particles to which the moist, fibrous mass has been applied can be effected according to various customary methods, such as freeze drying, vacuum drying or drying at atmospheric pressure. The pressure for this can vary in the range from 0.01 to 1.1 bar and the temperature in the range from −50 to 250° C., preferably from 0 to 200° C., particularly preferably from 120 to 180° C.

[0019] Another way of applying the moist, fibrous mass to the particles is to spray the mass onto the particles. This can be effected at between 50 to 400° C., preferably between 100 to 350° C., particularly preferably between 150 and 300° C., with simultaneous drying.

[0020] The calcination of the particle-fiber agglomerates can be carried out at pressures in the range from 0.01 to 1.1 bar and at temperatures in the range between 50 to 600° C., preferably between 100 to 450° C., particularly preferably between 150 to 350° C.

[0021] Calcination ensures partial or complete removal of volatile binders or swellants from the particle-fiber agglomerates.

[0022] The size of useful particles can vary within wide limits. In general, the particles, especially catalyst or catalyst support particles, will be from 0.01 to 10 mm, preferably from 0.05 to 5 mm and particularly preferably from 0.1 to 3 mm in size.

[0023] The particles, especially the catalyst or catalyst support particles, can have the form of tablets, annulae, calottes or extrudates such as granular, strand shape, star shape or any shape extrudates, spall form particles, sprayable powder or granules, including sprayable granules, but it is also possible to use spherical or irregularly shaped particles, or particles of any shape, produced according to other methods.

[0024] Useful particles further include particle-fiber agglomerates prepared according to the invention either by process A or preferably by process B.

[0025] Preparation Process B

[0026] Size Reduction of Large Particle-Fiber Agglomerates

[0027] Large particle-fiber agglomerates can be prepared by dispersing the fibers in a moist mass of particle powder with or without binders and with or without swellants. The moist mass may further contain pore-forming outburnable materials such as, for example, stearic acid or wood flour.

[0028] The moist mass obtained can be formed into large particle-fiber agglomerates according to customary methods, such as outpressing with piston presses, extruding and also by mechanical or hydraulic pressing, which are subsequently dried or partially dried.

[0029] The drying of the moist mass obtained can be effected according to various customary methods, such as freeze drying, vacuum drying or drying at atmospheric pressure. The pressure for this can vary in the range from 0.01 to 1.1 bar and the temperature in the range from −50 to 250° C., preferably from 0 to 200° C., particularly preferably from 120 to 180° C.

[0030] The dried or partially dried large particle-fiber agglomerates can be further consolidated by a further pressing operation, such as mechanical, hydraulic or isostatic pressing (afterpressing). Afterpressing can be used to modify the geometric shape of the large particle-fiber agglomerates.

[0031] Afterpressing can also be applied to particle-fiber agglomerates according to the invention which were prefabricated according to preparation process A or B.

[0032] The dried or partially dried or afterpressed large particle-fiber agglomerates can be size reduced to the desired particle-fiber agglomerates by methods or processes of predominantly breaking, crushing or tearing and less of a cutting character to create fracture facets from which fibers protrude. Useful size reduction means include for example jaw, round, roll and hammer crushers, hammer, impact and impact disk mills and also beater and pin mills. It is also possible to use combinations of various size reduction means. Size reduction can take place in one or more stages.

[0033] Any volatile binders or swellants or outburnable materials present can be partially or completely removed by calcination. Calcination can take place before or after size reduction. When the aforementioned afterpressing is employed for the larger particle-fiber agglomerates, calcination can take place before or after the afterpressing.

[0034] It is also possible to effect calcination in plural stages, for example before and after the afterpressing and also before and after the size reduction.

[0035] Calcination can be carried out in one or more stages at pressures in the range from 0.01 to 1.1 bar and at temperatures in the range from 50 to 700° C., preferably from 100 to 500° C., particularly preferably from 150 to 350° C.

[0036] The particle size of the particle-fiber agglomerates obtainable by the production process B can be varied within wide limits. Generally they have the form of spall and generally the particle sizes are in the range from 0.01 to 10 mm, preferably in the range from 0.05 to 5 mm, particularly preferably in the range from 0.1 to 3 mm.

[0037] Useful particles or particle powders include generally all elements (and their compounds and also their alloys or mixtures) from which solid particles can be prepared, preferably all elements (and their compounds and their alloys or mixtures) from which solid particles can be prepared and where diffusion processes in the solid particles play a part in their use, particularly preferably all elements (and their compounds and also their alloys and mixtures) from which solid particles can be prepared and where diffusion processes and/or catalytic processes or chemical processes in or on the solid particles play a part in their use.

[0038] Useful particles or particle powders include for example molecular sieves or adsorbents such as zeolites or aluminosilicates for gas drying and gas purification, particularly preferably catalyst materials or catalyst supports to which catalytically active components may be applied by saturating or coating.

[0039] The catalyst material can consist of or comprise Cu, Zn, Fe, Ni, Co, V, Mo, W, Si, Mg, Al, Ma, Mn, Ba, Cr, Pd, Pt compounds, preferably their oxides, hydroxides, carbonates or hydroxycarbonates or their mixtures.

[0040] Useful catalyst supports include for example silicon dioxide, aluminum oxide, magnesium oxide, titanium dioxide, zirconium dioxide, zinc oxide or their mixtures and also their silicates, aluminates, carbides or other inorganic compounds.

[0041] Suitable organic particles or particle powders include ion exchange resins, for example ion exchange resins based on phenol, styrene, acrylic acid resins (Duolite™, Lewatite™, Amberlite™).

[0042] The fibers of the particle-fiber agglomerates according to the invention have the structure of individual fibers, fiber bundles, fiber tufts or their mixtures, but are preferably not wovens, loop-drawn knits, mats, networks, webs or three-dimensional fibrous structures. Useful fibers include glass fibers, ceramic fibers, carbon fibers, graphite fibers, polymer fibers, metal fibers or their mixtures.

[0043] Useful materials for the ceramic fibers include for example silicon carbide, aluminum oxide, aluminum silicate or their mixtures.

[0044] Useful polymer fibers include for example polyamide, aramid, acrylic fibers.

[0045] Useful metal fibers include all metals from which fibers can be made, for example copper, aluminum, nickel, cobalt, iron, tungsten, silver or their alloys or their mixtures and also steel in its various varieties.

[0046] The fibers used can be varied within wide limits with regard to length and diameter. Generally the fibers would be from 0.1 to 20 mm, preferably from 0.5 to 10 mm, particularly preferably from 2 to 6 mm, in length and from 0.5 to 100 microns, preferably from 2 to 50 microns, particularly preferably from 5 to 20 microns, in diameter.

[0047] Useful binders include generally all known binders, such as inorganic binders, for example cement, lime, gypsum, Al₂O₃, SiO₂ and also sols or mixtures thereof, or organic binders, for example cellulose, methylcellulose, starch, polyethylene oxides, polyvinyl alcohols, polyurethanes, styrene-butadiene copolymers, polyamide-polyamine copolymers, resins such as epoxy resins, acrylic resins, urea-formaldehyde resins, melamine-formaldehyde resins, epichlorohydrin resins or phenolic resins, glues such as phenolic resin glues or mixtures thereof or mixtures of inorganic and organic binders, and organic binders can be partially or completely or substantially completely removed from the particle-fiber agglomerates, for example thermally.

[0048] Useful swellants generally include all known swellants, such as inorganic swellants or preferably organic swellants, for example carboxymethylcellulose, polyacrylic and polymethacrylic compounds or mixtures thereof, and organic swellants can be partially or completely or substantially completely removed from the particle-fiber agglomerates, for example thermally.

[0049] The immobilization by the fibers protects the solid particles against mechanical stresses due to shaking or vibration and prevents egress of solid particles when liquids or gases flow through a fixed bed formed from the particle-fiber agglomerates according to the invention.

[0050] The particle-fiber agglomerates according to the invention which include catalytically active particles are particularly useful for packings flowed through by liquids or preferably gases.

[0051] When the particles are catalytically active, the particle-fiber agglomerates according to the invention are generally useful for all suspension-catalyzed or preferably heterogeneously catalyzed reactions, for example for oxidation reactions, reductions, redox reactions, conversions, hydrogenations, hydroformylations, exhaust gas cleanups, dehydrogenations, alkylations, condensations, cracking processes, etherifications, esterifications, isomerizations, selective hydrogenations or syntheses.

[0052] Different fibers can be selected according to the catalyst's applications and the prevailing application conditions. Metal fibers are particularly useful for applications where heat is introduced or removed from the fixed bed consisting of the particle-fiber agglomerates according to the invention.

[0053] The particle-fiber agglomerates according to the invention which include catalytically active particles are useful as catalyst packings for all reaction spaces which are customarily used for fixed bed catalysts, such as tubes, cages or netty containers and all reactors such as all commonly used reactor types in which beds or, for example, comb-shaped catalysts are used, for example cylindrical reactors, tube bundle reactors, crossflow reactors and reactors for automotive catalytic converters.

[0054] Applications where catalysts are customarily used for suspension, moving bed or fluidized bed processes can be practised by using instead a fixed bed formed from the particle-fiber agglomerates prepared according to the invention and which is flowed through by each of the liquids or gases to be treated in the process.

[0055] The particle-fiber agglomerates according to the invention can be used to pack any vessel or reactor. Owing to the resilient properties due to the fibers protruding from or surrounding the solid particles, the act of packing can be likened to one of stuffing the vessels or reactors full. The solid particles can be very small. They are kept spaced apart by the fibers, so that adequate perviousness to liquids or gases can be ensured.

[0056] The particle-fiber agglomerates according to the invention which include catalytically active particles hold the catalyst particles spaced apart by their fiber content and pack out the catalyst space to such a degree that, owing to the flexibility of the fibers, the catalyst space is always substantially uniformly packed out with catalyst. This minimizes the degree to which compounds which are to be reacted over the catalyst can bypass the catalyst without any reaction. The particle-fiber agglomerates according to the invention are advantageous in stationary, but especially in mobile, applications such as catalysts for fuel cells and engine exhaust gas cleaning.

[0057] The fiber content of the particle-fiber agglomerates according to the invention can be varied within wide limits. It is generally in the range from 0.1 to 20% by weight, preferably in the range from 0.2 to 10% by weight, particularly preferably in the range from 0.5 to 5% by weight.

EXAMPLES

[0058] Production Process A

Example 1A

[0059] First 7 g of polyethylene oxide (Alkox™ E-160, Meisei Chemical Works LTD., Kyoto, Japan) and then 7 g of polyacrylate (Aqualic™ CAW3, BASF AG Ludwigshafen) were dissolved in 1 l of completely ion-free water at room temperature by stirring in a beaker. After a stirring time of 15 minutes, the viscid liquid was transferred into a Sigma kneader (Werner & Pfleiderer). After addition of 300 g of aluminum sol (Disperal™ Sol P2, Condea) and a kneading time of 5 minutes, 20 g of carbon fibers (Sigrafil™ SFC-3-GLB SGL Technik GmbH, 86405 Meitingen) were kneaded into the mass in the course of 15 minutes.

[0060] A further Sigma kneader (Werner & Pfleiderer) was used to moisten 2400 g of a catalyst spall consisting of 60% by weight of copper oxide, 30% by weight of zinc oxide and 10% by weight of aluminum oxide, sieve fraction 0.15 to 0.4 mm, with 360 g of completely ion-free water. After a mixing time of 5 minutes in the kneader, the above-described fiber-containing kneaded mass was introduced into the kneader which contained the incipiently moistened catalyst spall. After a mixing time of 5 minutes, the mass obtained was removed from the kneader and dried in a drying, cabinet at 120° C. for 5 hours. Thereafter, the dried mass was calcined in a through air oven at 300° C. and atmospheric pressure for 1 h.

[0061] The particle-fiber agglomerates thus obtained contained 93.42% by weight of catalyst spall, 5.8% by weight of aluminum oxide and 0.78% by weight of carbon fibers.

[0062] When a cylindrical vessel was stuffed by hand using a tamper, a packing weight of 700 g/l was obtained.

Example 2A

[0063] Example 2A corresponds in all details to Example 1A except for one difference.

[0064] The difference concerns the type of fibers used. Instead of carbon fibers, example 2A utilized 30 g of stainless steel fibers (Bekishield™ GR 90/CO2/5 PVA Bekaert Faser Vertriebs mbH, 65510 Idstein).

[0065] The particle-fiber agglomerates thus obtained contained 93.04% by weight of catalyst spall, 5.8% by weight of aluminum oxide and 1.16% by weight of steel fibers.

[0066] When a cylindrical vessel was stuffed by hand using a tamper, a packing weight of 570 g/l was obtained.

[0067] Production Process B

Example 1B

[0068] First 12.5 g of polyethylene oxide (Alkox™ E-160, Meisei Chemical Works LTD., Kyoto, Japan) and then 12.5 g of polyacrylate (Aqualic™ CAW3, BASF AG Ludwigshafen) were dissolved in 1 l of completely ion-free water at room temperature by stirring in a beaker. After a stirring time of 15 minutes, the viscid liquid was transferred into a Sigma kneader (Werner & Pfleiderer). After addition of 500 g of catalyst powder consisting of 60% by weight of copper oxide, 30% by weight of zinc oxide and 10% by weight of aluminum oxide having an average particle size of 80 microns and also addition of 50 g of carbon fibers (Sigrafil™ SFC-3-GLB, SGL Technik GmbH, 86405 Meitingen), the batch was kneaded for 3 minutes. Thereafter, the kneader was supplied with a further 1500 g of catalyst powder in three portions of 500 g each, which were each kneaded in for 3 minutes.

[0069] The kneaded mass was formed into 16 mm extrudates using a piston press. The internal diameter of the barrel of the piston press was 65 mm, the molding pressure was 130 bar.

[0070] The formed 16 mm extrudates were dried in a drying cabinet at 120° C. for 12 hours. The dried extrudates were wrapped in thin latex sheaths and afterpressed in an isostatic press at 1500 bar.

[0071] The afterpressed strands were calcined in a through air oven at 300° C. and atmospheric pressure for 1.5 hours.

[0072] The calcined extrudates were precomminuted with a mortar and pestle to particles 2 to 5 mm in size and then further comminuted in three stages in a roll crusher.

[0073] The roll crusher (from Bauermeister, roll diameter 250 mm, roll width 80 mm, smooth rolls) had the following settings:

[0074] 1st stage: roll nip 2 mm, 2nd stage: roll nip 1 mm, 3rd stage: roll nip 0.25 mm. The peripheral speed of the rolls was set to 5 m/s in all three stages.

[0075] The particle-fiber agglomerates thus obtained contained 97.5% by weight of catalyst powder and 2.5% by weight of carbon fibers. When a cylindrical vessel was stuffed by hand using a tamper, a packing weight of 1000 g/l was obtained. 

We claim:
 1. Particle-fiber agglomerates, characterized in that these agglomerates comprise fibers having the structure of individual fibers, fiber bundles, fiber tufts or mixtures thereof with firmly adhering particles.
 2. Particle-fiber agglomerates as claimed in claim 1, wherein the fibers are glass fibers, ceramic fibers, carbon fibers, graphite fibers, polymer fibers, metal fibers or mixtures thereof.
 3. Particle-fiber agglomerates as claimed in claim 1 or 2, wherein the particles comprise inert material, catalytically active material or mixtures thereof.
 4. A process for preparing particle-fiber agglomerates as claimed in any of claims 1 to 3, which comprises a) fibers being mixed with a binder and associated with particles or b) fibers and particle powder being mixed in the presence or absence of a binder, pressed to form larger agglomerates and these being broken or hammered to pieces.
 5. The use of particle-fiber agglomerates as claimed in any of claims 1 to 3 as catalysts.
 6. The use of particle-fiber agglomerates as claimed in any of claims 1 to 3 as catalysts for mobile applications.
 7. The use of particle-fiber agglomerates as claimed in any of claims 1 to 3 as catalysts for fuel cells.
 8. The use of particle-fiber agglomerates as claimed in any of claims 1 to 3 as catalysts for exit gas cleaning. 